1. Field of the Invention
The present invention relates to laminated ceramic electronic components, and particularly relates to the structure of external terminal electrodes to be provided on the laminated ceramic electronic components.
2. Description of the Related Art
In recent years, the market for compact portable electronic devices, such as cellular phones, notebook personal computers, digital cameras, and digital audio devices, has expanded. In the portable electronic devices, the size has been increasingly reduced and, simultaneously, the performance has been increasingly improved. A large number of laminated ceramic electronic components are mounted on portable electronic devices. There have demands on the laminated ceramic electronic components to reduce the size and improve the performance thereof. For example, it has been demanded of laminated ceramic capacitors to reduce the size and increase the capacitance.
As a measure for reducing the size and increasing the capacitance of laminated ceramic capacitors, it is effective to reduce the thickness of a ceramic layer to form a thin ceramic layer. Recently, ceramic layers having a thickness of about 3 μm have been put into practical use. At present, research is being conducted to find a way to further reduce the thickness of the layers of the multilayer capacitor. However, as the thickness of the ceramic layer has been increasingly reduced, short circuiting between internal electrodes is likely to occur, causing a problem in that it is difficult to secure the quality.
As another measure, a measure for increasing the effective area of the internal electrodes is mentioned. However, when laminated ceramic capacitors are mass-produced, it is necessary to secure the side margin between the internal electrodes and the side surfaces of a ceramic element assembly or the end margin between the internal electrodes and the end surfaces of the ceramic element assembly to some extent in consideration of lamination shift and cut shifting of a ceramic green sheet. Therefore, there is a limitation on increasing the effective area of the internal electrodes.
In order to increase the effective area of the internal electrodes while securing a given margin, it is necessary to increase the area of a ceramic layer. However, there is a limitation on increasing the area of the ceramic layer within a determined standard dimension and, moreover, the thickness of the external terminal electrode itself also serves as a hindrance.
Heretofore, the external terminal electrodes of the laminated ceramic capacitor are formed by applying and printing a conductive paste to the ends of the ceramic element assembly. As methods for applying a conductive paste, a method for immersing the ends of the ceramic element assembly in a paste tub containing a conductive paste, and then pulling up the same is used in most cases. However, according to the method, the conductive paste is likely to thickly adhere to the center of the end surfaces of the ceramic element assembly due to the viscosity of the conductive paste. Thus, the external terminal electrodes are partially thickened (specifically, exceeds 30 μm, for example), and thus the area of the ceramic layer is caused to decrease.
In view of the above, a method for directly forming external terminal electrodes by plating has been proposed (e.g., Japanese Unexamined Patent Application Publication No. 2004-327983). According to the method, when a plating film precipitates and grows on exposed portions of the internal electrodes on the end surfaces of the ceramic element assembly as the nucleus, exposed portions of adjacent internal electrodes are connected to each other. Therefore, the application of the method allows the formation of thin and flat external terminal electrodes compared with those obtained by former methods using a conductive paste.
Preferred embodiments disclosed in Japanese Unexamined Patent Application Publication No. 2004-327983 are classified into a first typical example (FIG. 7B in Japanese Unexamined Patent Application Publication No. 2004-327983) in which the plating films are formed while being limited to the end surfaces of a ceramic element assembly and a second typical example (FIGS. 8B and 10B in Japanese Unexamined Patent Application Publication No. 2004-327983) in which the plating films are formed so as to extend up to one portion of each of a pair of adjacent principal surfaces from the end surfaces of the ceramic element assembly. In the first typical example, an exposed conductive area serving as the nucleus for growing the plating films is not formed on a portion other than the exposed portions of the internal electrodes on the end surfaces of the ceramic element assembly. In the second typical example, an exposed conductive area serving as the nucleus for growing the plating film is formed also on, for example, a portion other than the exposed portions of the internal electrodes on the end surfaces of the ceramic element assembly.
However, the first typical example and the second typical example have problems to be solved.
First, in the first typical example, the distance from the ends of the plating films to the exposed portions of the internal electrodes is relatively short. Thus, a penetration path of moisture or the like from the outside to the inside of the ceramic element assembly through the internal electrodes becomes short, and thus sufficient humidity resistance reliability cannot be obtained in some cases.
In contrast, in the second typical example, the plating film is formed while projecting from the principal surface of the ceramic element assembly, causing a problem of impeding the reduction in the thickness of laminated ceramic electronic components.